The increased integration of semiconductor devices requires the formation of fine patterns having line widths of typically a quarter micron. Accordingly, lithography processes which employ deep ultraviolet ray (deep-UV) technology (248 nm) offer significant increases in resolution because of the shorter, and thus more energetic wavelengths used in comparison to conventional g-line (436 nm) and i-line (365 nm) rays.
A resist material for use in conjunction with deep-UV technology is referred to as a chemically amplified resist. In general, a chemically amplified resist typically comprises a resin containing a dissolution inhibiting group along with a photo acid generator (PAG). Upon exposure to light, an acid is generated by the PAG and acts as a catalyst to heighten the solubility of the resist when contacted by a developing solution. More specifically, the dissolution inhibiting group of the resin reacts with the acid so as to allow the resin to dissolve readily in developing solution. At the same time, the transparency of the resist during the light exposure is maintained.
One of the main factors in determining the performance of a chemically amplified resist is an index relating to the change in solubility of the resist before and after exposure to light. The difference in the solubility is determined by several factors. One of the factors relates to the decomposition rate of the dissolution inhibiting group contained on the resin in the presence of an acid catalyst which is activated by light. Another factor relates to solubility of the exposed resin in a developing solution.
In light of the above, resins have been sought which exhibit high decomposition rates upon exposure to light and high solubility levels in developing solutions. Additionally, resins not exposed to light should dissolve as slowly as possible in developing solutions. Such resins are typically manufactured by polymerizing a monomer containing a t-BOC (t-butoxycarbonyl) group. The presence of a t-BOC group is advantageous in that it is converted to a hydroxy group by acidolysis upon light exposure. The resist which contains the hydroxy group dissolves readily in developing solution. At the same time, the unexposed resin containing the unconverted t-BOC group does not easily dissolve in developing solution.
In spite of the desirable properties of the above resins, the resins can pose processing difficulties. Specifically, the resins often possess poor thermal stability. Since high temperatures are typically employed in resin processing, the resins often burn and decompose. Accordingly, there is a need in the art to provide resins which exhibit the desirable properties described herein while displaying adequate thermal stability.